Process for heat relaxing stretched polyamide filament



\ April 1, 1969 H. SPECKER ETAL 3,436,450

PROCESS FOR HEAT RELAXING STRETCHED POLYAMIDE FILAMENT Filed Jan. 19, 1965 I Sheet of 2 O QOOOOOOOOOOOO o oooooooooooeuo OOOOOOOOOOOOOOOO lnvenlor A Horneys April I, 1969 H. SPECKER ET AL 3,436,450

PROCESS FOR HEAT RELAXING STRETCHED POLYAMIDE FILAMBNT Filed Jan. 19, 1965 Sheet 2 of 2 oooooooaooooooooaoo 00 000 00 000 0000000 00000000000000 000000 Inventor #dj 0 be a Kc r D/ETE/CH MOHfiLE Jaw Mg 22 m Patented Apr. 1, 1969 3,436,450 PROCESS FOR HEAT RELAXING STRETCHED POLYAMlDE FILAMENT Hugo Specker and Dietrich Miihrle, Emmenbrucke, Lucerne, Switzerland, assignors to Societe de la- Viscose Snisse, Emrnenbrucke, Lucerne, Switzerland, a Swiss body corporate Filed Jan. 19, 1965, Ser. No. 426,608 Claims priority, application Great Britain, Jan. 28, 1964, 3,710/64 Int. Cl. 1329c 25/00; Dtllf 7/06 U.S. Cl. 264--237 7 Claims The present invention provides a process for relaxing stretched polyamide filaments so as to produce filaments of low and uniform tendency to shrink, and apparatus for use therein. The polyamide filaments produced in accordance with the invention produce stable packages and woven and knitted fabrics showing only little streakiness.

Broadly speaking, the process of the invention comprises causing stretched but unrelaxed filaments to move in a first circumferential path at at most 110 C., then in a second circumferential path of lower diameter and at a temperature of 120 to 200 C., then in a third circumferential path of lower diameter than the second but at a higher temperature between 130 and 210 C., and finally in a fourth circumferential path of diameter equal to that of the third such path in which the said filaments are cooled. In practice, using the form of roller described below, the new process comprises passing stretched but unrelaxed filaments round a roller made with its surface in three sections of successively decreasing diameter, the filaments being first passed at a temperature of at most 110 C. round the section of greatest diameter, then round the second and third sections of successively decreasing diameter and increasing temperature, the temperature of the second section being 120 to 200 C. and the temperature of the third section being 130 to 210 C., and final ly round a cooled portion of the third section.

The roller required for the new process comprises three co-axial sections of successively decreasing diameter, the section of greatest diameter and part of the section of least diameter being provided with cooling means and the intermediate section and part of the section of least diameter adjacent the section of intermediate diameter being provided with heating means such that the temperature of the surface of part of the section of least diameter can be kept higher than that of the section of intermediate diameter.

The filaments produced by the new process have a uni form, low residual shrinkage, and the invention includes within its scope the use of the new filaments for the manufacture of woven and knitted fabrics having good dimensional stability and little streakiness.

The terms residual shrinkage, heat-setting, relaxing and stabilising as used herein have the following meanings:

Residual shrinkage is the longitudinal contraction in boiling water, determined as follows. The banks are immersed for 2.0 minutes in boiling water and then dried under a load of 0.1 gram per denier.

Residual shrinkage 100 X (length before shrinking) (length after shrinking) length before shrinking It is generally known that freshly stretched filaments of synthetic thermoplastic resins display a considerable residual shrinkage. Freshly stretched filaments of polyhexamethylene adipamide (nylon 66) display a high residual shrinkage, which decreases over a prolonged period asymptotically to about 10%. This residual shrinkage is in general undesirable. Inter alia, owing to the aforementioned recovery very strong and substantial bobbins must be used in the stretching operation to enable them to withstand the shrinking forces involved. On such a bobbin the individual layers of filament recover irregularly because the layers in direct contact with the solid bobbin can contract only very little, whereas the outermost layers contract much more. This produces in the reeled filament shrinkage diiferences which result in streakiness of woven and knitted fabrics. Attempts have already been made to overcome these disadavantages by heat-setting and relaxing the filaments.

Heat-setting, performed for instance according to the method of United States patent specification No. 2,307,- 846, stabilises the length of the filament so that at temperatures below the heat-setting temperature no, or only minor, changes in length occur, even if the filaments or the woven or knitted fabrics made from them are heattreated in the slack state. Instead of, or in addition to, the heat-setting operation, a swelling treatment may be performed, but in heat-setting the woven or knitted fabrics to produce and maintain a given shape a temperature must be used in such a case that is higher than the first-setting temperature.

In many cases relaxing is performed by heating the filament on a flexible support or in the form of a tubeless wound package so that it can shrink freely; in this manner residual shrinkage values of less than 2% are achieved (United States specification No. 2,199,411). It has, however been observed that yarns having such low residual shrinkage values have disadvantages, for example a high stretch modulus, so that they lend themselves less readily to processing. Furthermore, it is hardly possible to produce stable package from such yarns. Thus, for example, in the book by Fourne, Synthetische Fasern, 1953, page 87, it has been stated that polyamide yarns for making stocking legs should, if possible, not be relaxed to a residual shrinkage below 6 to 7%. Even for technical fabrics, yarns having too much residual shrinkage are not suitable.

Accordingly, controlled relaxation has been resorted to so that yarns relaxed in this manner have a very minor final residual shrinkage deviating only little from the mean value. In addition relaxing Was carried out on the travelling filament and this offers a further advantage.

A variety of processes and devices for the controlled relaxing of yarns of synthetic thermoplastic resins have been described. Thus, for example, United States specifications Nos. 3.003,222 and 3,069,836 describe an unheaded roller having two sections of unequal diameter cooperating with several feed rollers, arranged after the stretching zone and requiring a separate heating device between the section of larger diameter and the section of smaller diameter. A similar one-step roller has been described in United States specification No. 2,956,330 and in French specification No. 1,206,907. These layouts are of little use on stretching machines which, as is known, have little spare space.

United States specification No. 2,807,863 similarly describes a combination of heat-stretching, relaxing and heat-setting cord made from polyhexamethylene adipamide, which requires a voluminous installation. Relaxing is carried out in one stage at a temperature ranging from to C.

Finally, British specification No. 656,631 discloses a process and a device for heat-stretching and relaxing filaments with the aid of a driven and a cooperating freely revolving roller having sections of different diameter, the heat treatment being performed on a heating slide. This proposal requires, however, substantial changes to be made to conventional stretching machines. In addition, the filament is not heated on a roller but on a heating slide.

It has been found that freshly stretched yarns of polyhexamethylene adipamide yarns of different counts shrink at a temperature above 120 C. within a fraction of a second. Relaxing on conical or heated rollers made in two sections produced only a minor reduction of the residual shrinkage since heat-setting occurred after only a few windings. It has also surprisingly been found that it is possible to reduce residual shrinkage to a fairly constant mean value of 2.5% by relaxing by a total of about 13% in 2 stages with an increasing temperature gradient on a roller made in three sections of decreasing diameter, heated to a maximum temperature of 210 C., without impairing the dyeing properties or the white content of the yarn. It is, however, of importance that the freshly stretched filament should not be heated to near the relaxing temperature.

One advantage of the invention is that it makes it pos sible to use stable package on a support that is inexpensive and does not have to satisfy extreme demands of resistance to compressibility, such as a tube of cardboard or a plastic material. To achieve this, the only stretching roller of the stretching machine--or when several such rollers are provided, the lastis replaced by the three section roller of the invention.

In the new process, it is convenient to stretch polyamide filaments in the first section of the roller, which has a maximum temperature of 110 C. and the largest diameter. In the second and third sections the filaments are ordinarily relaxed to a total of to (Hereinafter these two sections are alternatively referred to as the first and second relaxing zones.)

Filaments suitable for use in the new process preferably consist of polyhexamethylene adipamide or polycaprolactam, but other polyamides or other thermoplastic polymers can also be used. The filaments may have any desired final count, for example from 15 to 2000 denier (1.7 to 222 tex). For stocking yarns, for example for doubled tops, filaments having a count of 40 denier (4.4 tex) are suitable. Those suitable for woven and knitted fabrics have a final count within the range of 15 to 300 denier (2 to 33 tex). For technical fabrics to be subsequently coated, for example tarpaulins, counts ranging from 210 to 1680 denier'(23 to 185 tex) are usual, whereas for heavy fabrics counts above 1100 denier (121 tex) are usual. The threads may consist of monofils. or multifils, depending on the ultimate purpose.

Stretching is advantageously carried out with a stretching pin. For threads of polyhexamethylene adipamide having a final count higher than 200 denier (22 tex) hotstretching may be used, for which purpose heating slides may be provided between the stretching pin and the roller, the thread being guided over them.

To prevent slip, the thread is wound 2 to 4 times round the first section of the roller and the cooperating feed roller. The axes of these rollers are slightly offset to ensure that the thread travels forward on these rollers in known manner. The temperature of the first section of the roller must not exceed 110 C., and this can be ensured by adequate air cooling or insulation. When the cooling is satisfactory, the surface of the stretching zone hardly reaches 90 C. at a normal draw-off speed of 400 metres per minute.

The degree of stretch can be adjusted within wide limits and depends on the spinning conditions and on the use to which the relaxed filaments are to be put.

When stretching is performed with the use of heat, it has a certain influence on the subsequent relaxation. However, the stretching and relaxing conditions may readily be matched by one skilled in the art within the limits of the invention.

As stated above, a positive temperature gradient is required between the second and third sections of the roller to prevent any heat-setting taking place before the third section. This temperature difference should advantageously be at least 10 C. but, when a suitable roller design is used, it may be up to 50 C. For the same purpose it is of advantage when the filament passes round the first relaxing zone only once or at most twice. The total relaxation, determined by the difference between the diameters of the individual sections, may range from 10 to 15% and depends on the ultimate use of filaments. In actual practice a lower limit of 2.5% residual shrinkage can and should be maintained. The upper limit of the residual shrinkage is probably about 7% using the temperature limits required for the performance of the invention. In general, taking into account the temperatures indicated above, a total relaxation of 13 to 14% is generally preferred. This value may apply to the two relaxing zones in 7 different proportions, and favourable results are obtained when, for example, two-thirds of the overall relaxation is carried out in the first relaxing zone.

Preferably the diameter of the section of greatest diameter is :5 mm. that of the section of intermediate diameter is 91:4 mm. and that of the section of least diameter is 87:4 mm.

The filament is wound 3 to 8 times round the third section of the roller and the associated zone of the feed roller, the best value for the precise number of times being found by preliminary experiment. While keeping the tension constant, the filament is then cooled by being wound 2 to 5 times round a cooled part of the third section and is finally reeled under a moderate tension. The temperature of the cooled zone should be as low as possible. In general, the roller itself will provide sufficient cooling, but when very thick filaments are made, there is no objection to providing additional cooling, for example by blowing cold air onto the filament. When the filaments are reeled on ring twisting spindles the reeling speed is adjusted in known manner by the weight of the traveller to suit the speed of rotation of the spindle and the ring diameter.

As mentioned above, the residual shrinkage may vary from 2.5 to 7% with a maximum deviation of :0.3% from the mean value per packages. The filaments form stable packages that are easy to unwind and can be stored for any length of time. In woven and knitted fabrics made from them, the filaments produce little streakiness and ensure excellent dimensional stability of these fabrics. For an equal drawing rate applied to the filaments the elasticity of the woven and knitted fabrics made therefrom is superior to that obtained with unrelaxed filaments so that the practical value of many finished products is appreciably improved.

The roller of the invention, which is intended to replace the stretching roller of a stretch-twisting frame, consists of three sections: The first section, which acts as a. conventional stretching roller, has the largest diameter. This zone may consist, for example, of a collar of a plastic material which is resistant to wear and tear and is a poor heat conductor, or it may taken the form of a metal collar which makes pointwise contact with the roller body. In addition, the collar may be cooled by an air current produced or assisted by transverse or longitudinal ribs. Furthermore, the collar may have radial bores through which cooling air can escape outwards during rotation of the roller.

The second preferably narrow, section has a smaller diameter than the first and constitutes the first relaxing zone.

The third section of the roller has a smaller diameter than the second section and is in part the second relaxing zone. Inside this zone there is advantageously provided an electric heater so that in operation it has a higher temperature than the second section. Part of the third section acts as a cooling zone. As in the first section, the cooling may be achieved by longitudinal or transverse cooling ribs and radial bores. The accompanying drawings illustrate a few variants of the device according to the present invention; where FIGURE 1 is a diagram of a commercial stretch-twisting frame;

FIGURE 2 is a roller in accordance with the invention with a plastic collar in the stretching zone; and

FIGURE 3 is a roller in accordance with the invention with a metal collar in the stretching zone together with its associated feed roller.

In FIGURE 1, the spinning bobbin 1 is fed by the spinning machine and placed on the stretch-twisting frame; the yarn is unwound over the top of the bobbin. The yarn runs over a yarn guide 2 through the supply device 3 consisting of a pair of rollers, round the stretching pin 4 and onto the draw-off unit consisting of feed roller 5 and stretching roller 6 past which it is guided by a further yarn guide 7 and by means of the traveller 8 twisted on a ring twisting spindle 9 and 10 and finally reeled.

FIGURE 2 illustrates a roller 6A according to the invention, the upper half being shown in section and the lower half in side elevation. The roller 6A is composed of the roller body 11 (seating on a spindle not shown in the drawing) and the plastic collar 12 shrunk onto it. The plastic collar 12, which accepts the freshly stretched filament, has the largest circumference. The roller body 11 has a first, narrow step and a second, wider step 13, a cavity 14 for fitting an electric heating coil and a thinner end portion 15, which is perforated to provide intense cooling and has a diameter equal to that of the second relaxing step 13.

The plastic collar 12 should advantageously make only pointwise contact with the roller body 11 to prevent as far as possible any transfer of heat to the freshly stretched filament. Alternatively, the collar may be designed so that it is cooled in operation by the air flowing past it.

FIGURE 3 illustrates another variant of a roller 6B in accordance with the invention with its associated feed roller 5. The upper half of the roller is shown diagrammatically in section, whereas the lower half is shown in side elevation. The roller 68 is attached via a thermal insulation 17 to a spindle 16. It is composed of the roller body 18 which is polished externally and has inside a cavity 19 to accept an electric heating unit 20. The roller body 18 carries on a thermal insulation 21 a polished metal ring 22 which is internally cooled in operation by circulating air. To improve the air circulation further, the metal ring may additionally be provided with radial bores (not shown) distributed over its whole surface. The metal ring 22 has the largest diameter and is used to accept the freshly stretched filaments. The roller body 18 has a narrow first relaxing zone 23, a wider second relaxing zone 24, and an open end portion 25 which has internal cooling ribs 26 and radial cooling bores; the diameter of the latter is equal to that of the second relaxing zone 24.

The following examples illustrate the process of this invention.

Example 1 A thread of polyhexamethylene adipamide consisting of 13 monofils. is stretched for experimental purposes by 323% on a conventional stretch-twisting frame with the use of a stretching pin at a speed of 440 in. per minute at the bobbin. The count of the reeled, stretched thread is 40 denier (4.4 tex) [=Thread A]. The weight of the traveller used is 0.04 gram, the spindle rotates at 7800 revolutions per minute and the ring diameter is 12.5 cm.

Another thread of polyhexamethylene adipamide, consisting of 13 monofils., is stretched by 323% on the same stretch-twisting frame, but in this case the conventional stretching roller has been replaced by a roller as shown in FIGURE 2 of the accompanying drawings. The thread coming from the stretching pin is wound twice round the cooled first section of the roller, which has a surface temperature of 81 C. and a diameter of 101.2 -mm., and round the associated zone of the feed roller. The thread is guided as shown in FIGURE 1. After the stretching, a two-stage relaxation is performed. In the second section of the roller, which has a diameter of 92.1 mm., the thread is relaxed by 9% at a surface temperature of 150 C. and in the third section, which has a diameter of 88.8 mm., it is relaxed by another 3% at a surface temperature of 162 C. The first relaxing zone and the associated zone of the feed roller is traversed once by the thread and the second relaxing zone four times. Finally, the thread runs twice round the cooling zone of the third section (having a surface temperature of 130 C.) together with the associated zone of the feed roller and is then reeled on cops at a speed of 440 metres per minute under the same conditions as for the unrelaxed thread [=Thread B]. The number of windings is determined in known manner by the offset angle between the two rollers, the width of the thread and the width of the individual zones.

Two further identical starting threads as in the precedingexperiment are stretched and relaxed in the manner described above but with the following surface temperature [=Threads C and D].

Thread 0 Thread D Stretching zone 83 85 Relaxing zones (maximum, about). 169 176 Cooling zone 135 141 The properties of the threads A to D are shown in the following table:

Residual shrinkage, unrecovered, from waist to tip of cop (percent) 11:1:08 3.0:];03 3.2i0.3 3.2;b0.3

The temperature difference between the two relaxing stages ranges from 10 to 30 C.

The above table shows that it is possible to obtain by the new process low and uniform residual shrinkage values. The relaxed threads are very suitable for making doubled tops of stockings. The textile products made therefrom can be dyed evenly and possess excellent dimensional stability.

When the relaxing is carried out with the same device at a temperature outside the range required for the performance of the present process, for example at C. or 230 C., the yarn runs badly and many ruptures occur.

Example 2 The experiments described in the foregoing example were repeated under slightly modified conditions with a coarser thread, consisting of 34 monofils., from polyhexamethylene adipamide containing 0.3% of titanium dioxide, in a manner such that a thread was obtained which had a count of about 210 denier (23 tex) and an elongation at break of about 19 to 24%. In all, four variants were relaxed under different conditions and each was reeled on cops at a speed of 266 metres per minute on a ring twisting spindle revolving .at 5400 rpm. with the aid of a ring of 12 cm. diameter and a traveller weighing 0.26 gram. The following table shows the relaxing conditions and the results that can be achieved in this manner:

The drawing rate applied to the relaxed threads was intentionally chosen higher so as to arrive at an elongation at break comparable with that of the relaxed threads.

The relaxed threads possess greater tensile strength and display a low and uniform residual shrinkage. They are suitable for a variety of technical purposes in which a very minor residual shrinkage is of importance.

Example 3 Polycaprolactam threads, containing 34 monofils, are stretched as described in Example 2, except that the second relaxing zone has a diameter smaller by 4% than the first, and are then reeled under the temperature conditions given below so that a thread is obtained which has a count of about 230 denier (25 tex).

cessive circumferential paths defined by four successive portions of a roller along the length of the roller, the filaments being stretched by movement in the first path which is at a temperature of at most C., then being relaxed while moving in the second path which is of smaller diameter than the first at a temperature of to 200 C., then being further relaxed while moving in the third path which is of smaller diameter than the second at a temperature at least 10 C. higher than the temperature of the second path and of to 210 C., and finally being cooled in the fourth path which is of the same diameter as the third.

2. Process according to claim 1 in which the third circumferential path has a diameter from 10 to 15% less than that of the first circumferential path.

3. Process according to claim 2 in which the second circumferential path has a diameter greater than that of the third by about one-third of the difference in diameter of the first and third circumferential paths.

4. Process according to claim 3 in which the filament moves 2 to 4 times round the first circumferential path, once to twice round the second circumferential path, 3 to 8 times round the third circumferential path, and 2 to 5 times round the fourth circumferential path.

5. Process according to claim 1 in which the temperature difference between the second and third circumferential paths is 10 to 50 C.

6. Process according to claim 1 in which the filaments are of polyhexamethylene adipamide.

7. Process according to claim 1 in which the filaments are of polycaprolactam.

Relaxing temperature in the 2nd relaxing stage C.) 0 120 Tensile strength (g./denier) 6.4 5. 61 .21 6. 27 6. 42 Elongation at break (percent). 23. 1 22.6 24. 25. 6 23. 6 Residual shrinkage (percent)- 9.45:0.4 8.6102 7.45:0. 05 6.63:0.1 7. 0i0.1 Percent degree of stretch 419 440 440 440 440 The difference in temperature between the first and the 40 References Cited second relaxing stage is 10 to 25 C. UNITED STATES PATENTS A thread treated in the second relaxing stage at a temperature of 110 C. could not be made to run smoothly 3,018,608 H1962 Kleekamm et 2871.3 because it wrapped itself repeatedly round the roller 3,221,385 12/1965 Stanley 28--62 owing to insufficlent relaxation. 45 FOREIGN PATENTS The thread relaxed in the second relaxing stage at 120 C. still displays a rather high residual shrinkage. Under the indicated conditions the optimum relaxation is achieved at a temperature of 160 C. in the second relaxing stage.

We claim:

1. Process for the manufacture of polya mide filaments of low and uniform tendency to shrink which comprises causing freshly stretched filaments to move in four suc- US. Cl. X.R. 

1. PROCESS FOR THE MANUFACTURE OF POLYAMIDE FILAMENTS OF LOW AND UNIFORM TENDENCY TO SHRINK WHICH COMPRISES CAUSING FRESHLY STRETCHED FILAMENTS TO MOVE IN FOUR SUCCESSIVE CIRCUMFERENTIAL PATHS DEFINED BY FOUR SUCCESSIVE PORTIONS OF A ROLLER ALONG THE LENGTH OF THE ROLLER, THE FILAMENTS BEING STRETCHED BY MOVEMENT IN THE FIRST PATH WHICH IS AT A TEMPERATURE OF AT MOST 110*C., THEN BEING RELAXED WHILE MOVING IN THE SECOND PATH WHICH IS OF SMALL DI- 